Generally, treadmills measure the distance a user travels indirectly, by measuring the speed of the treadmill belt, and integrating the speed over a particular time. The number of calories burned by a user is estimated based on the distance the treadmill belt travels at a particular speed and/or treadmill belt slope.
More sophisticated treadmills may provide monitoring of user vital statistics, such as a heart rate, using a contact sensor such as a grip sensor, or wireless heart rate monitor worn by the user. However, grip sensors require a user to hold a conductive region of the treadmill for a significant time to permit the sensor to read electrical signals in the user's hands. Similarly, wireless heart rate sensor must be worn by a user with a sensor on the wireless device in contact with the user to acquire the heart rate. Additionally, the contact-type vital sensors are limited to sensing heart rate, and cannot provide information on other vital statistics.